1. Field of the Invention
The present invention relates to a motor device, and in particular relates to a wiper motor for an automotive vehicle.
2. Prior Art
A typical known such motor device is, for example, the one shown in U.S. Pat. No. 5,203,219 (corresponding to Japanese Patent Application Laid-Open No. 4-292244). This device is shown in FIG. 4.
Referring to this Figure, a worm 102 is housed within a hollow casing 100 and is rotated along with the turning of a motor by being connected to a motor shaft thereof. A worm wheel 104, for which a rotational shaft 104a functions as a central axis, is meshed with this worm 102 and is rotated thereby at a reduced rotational speed. Further, a crank pin 106a is formed integrally with this worm wheel 104. A linking rod system 106 is connected to this crank pin 106a and converts the continuous rotational motion of the crank pin 106a into reversible rotational motion of an output shaft 112a.
Further, this linking rod system 106 comprises a sector shaped gear 112 which is connected to the output shaft 112a. Moreover, it comprises a crank arm 110 which functions as a sector rod, one end of which is meshed with the sector shaped gear 112 and the other end of which is supported on the crank pin 106a so as to be rotatable around the axis thereof.
Furthermore, a pair of link plates 114 and 116 which support the region of meshing in the thickness direction are included. The one ends of these link plates 114 and 116 are supported by a shaft 118 while their other ends are supported on the output shaft 112a, and together with the shaft 118 these link plates 114 and 116 execute oscillatory motion to and from around the output shaft 112a.
Furthermore, a thickened portion 120 is formed upon an inner wall of a cover 101 of the hollow casing 100, so as to be in contact with the linking rod system 106. In this construction, this thickened portion 120 is mainly formed over the entire circular path over which the crank pin 106a is moved and over a circular shaped region concentric to and surrounding the output shaft 112a.
However, the following problems arise in connection with the above described prior art motor device.
(1) Except for the region over which the crank pin 106a is rotated and the region around the end of the output shaft 112a, the thickened portion 120 is not formed over the regions adjoining the shaft 118 (and in particular over the aforementioned meshing region which is supported by the link plates 114 and 116), and accordingly an empty space 122 is left between the cover 101 and the link plate 114 and the shaft 118.
Because of this, the sector shaped gear 112 is subjected via the output shaft 112a to a considerable load in the direction shown in FIG. 4 by the arrow Z when a windshield and a wiper fitted to the output shaft 112a which are not shown in the figures are in contact and the wiper is pressed against the windshield. This causes a force (an offset load) to be imparted to the link plates 114 and 116 which tends to break the meshing engagement between the crank arm 110 and the sector shaped gear 112, and because of this the rotation of the rotation shaft 104a is not satisfactorily transmitted to the output shaft 112a. Because of the above described load, the crank arm, the sector shaped gear and so on vibrate and cannot rotate smoothly, and cannot execute stable motion, and noise is generated by this vibration.
Further, even if the thickened portion 120 is formed on the cover 101 over the region thereof above the link plate 114, then a new problem arises that the thickened portion 120 need to be made correspondingly thick and also large to have enough strength. Additionally, the requirement to provide this new dedicated member means that the number of parts is increased and the cost is higher.
(2) Except for the worm wheel 104, all of the parts are made from steel, and thus the sliding action between the parts which mutually slide against one another--in particular between the rotation shaft 104a and its bearing (not shown in the figure), between the crank arm 110 and the crank pin 106a, between the output shaft 112a and its bearing (not shown in the figure), and so on--is metal to metal sliding motion, and accordingly undue noise is caused during operation by vibration.
(3) Furthermore it might be contemplated, as a measure for solution of the above described problem (2), to fit wave washers or fixing rings for preventing detachment to the above-described portions which are in mutual sliding motion, but it would be necessary to provide a large number of such members as described above, and it is considered that this would increase the number of parts in the construction and would unduly increase the cost.
(4) The end portion 113 of the output shaft 112a is in contact with inner wall of the cover 101, and the end portion 107 of the crank pin 106a is in contact with the thickened portion 120 of the cover 101. Accordingly, there is the problem that if the paths are pursued in sliding motion over a long time period in a small contact area then the cover 101, which is made of resin, will become grooved by the sliding motion between the metallic output shaft 112a and itself and by the sliding motion between the crank pin 106a and itself.
Yet further, although for example related motor devices such as that disclosed in German Patent DE3247421 and the like have been proposed, since in these exemplary prior arts as well a space is present above the output shaft and the meshing portion, they do not solve the problem described above under
(1). In addition, although various motor devices have been proposed in German Utility Model DEG8001379, Japanese Utility Model Application Laid-Open No. 5-52421, Japanese Utility Model Application Laid-Open No. 4-69358, Japanese Utility Model Application Laid-open No. 4-127061, and the like, none of these prior art proposals mentions the above problems (1) to (4) at all.